According to a technique using the EUDCH that is a high-speed packet transmission channel on an uplink according to the W-CDMA, data is transmitted from a mobile station by configuring a control channel and a data channel and multiplexing codes (see, for example, Non-Patent Document 1). It is, therefore, possible to configure a power on the control channel and that on the data channel independently of each other.
However, a maximum transmission power of the mobile station is limited and data decoding cannot be performed unless a control signal is accurately received. For this reason, the mobile station allocates a necessary power first to the control channel so as to transmit the control channel with a required quality. The mobile station then calculates a remaining power, decides a transmission rate at which a power is equal to or lower than the remaining power as a transmission rate on the data channel, and transmits the control channel and the data channel. Accordingly, if the power used on the control channel is lower, the power that can be used on the data channel is increased, making it possible to select a higher transmission rate.
Meanwhile, the control channel according to the EUDCH includes a plurality of pieces of control information different in required quality. If a transport format (TF) indicating information on a transmission form (e.g., a block size) of data transmitted on the data channel and a scheduling information (SI) necessary for a base station to perform scheduling are transmitted on the control channel, and the base station erroneously receives the TF, the data cannot be decoded. Due to this, an error rate required for the TF is normally set more strictly than that required for the SI.
FIG. 10 is an explanatory view of one example of a control signal transmission method according to a conventional art. As stated, on a control channel shown in FIG. 10, a transmission power in a signal field of the TF (TFCI) is configured higher than that in a signal field of the SI, and the TF is transmitted so that a power per bit of the TF is higher. By doing so, even if different required qualities are set for the respective control signals, the control signals can be transmitted on the same channel while satisfying the respective required qualities.
Moreover, transmission of a control signal (TXI: Transmission Indicator) for efficiently using hardware resources of a mobile station is considered (see, for example, Non-Patent Document 2). FIG. 11 is an explanatory view of another example of the control signal transmission method according to the conventional art. Referring to FIG. 11, the TXI is a control signal which is used only during soft handover and the transmission of the TXI is stopped in regions other than soft handover regions.    Non-Patent Document 1: TR25.808v1.0.0 (2004-12n) 3rd Generation Partnership Project: Technical Specification Group Radio Access Network; FDD Enhanced Uplink; Physical Layer Aspects (Release 6)    Non-Patent Document 2: 3GPP RAN WGI #38bis Meeting R1-041066, Sep. 20-25, 2004, “Uplink Control Channel Design for Enhanced Uplink”, Motorola    Patent Document 1: JP-A-2003-229835    Patent Document 2: JP-A-8-316967